In our modern society, it has become ever more important for monitoring our environment and providing early sign of environmental changes that may affect health or even life of its inhabitants. With that, there is a growing demand for new technology of making various environmental sensors. Particularly, there is an acute need for sensing environmental hazardous substances such as volatile organic compounds (VOCs). Environmental sensors are also important for quality control in the food, beverage, and fragrance industries, for assessment of odor sources (e.g. wastewater, livestock, and landfill), or for industrial bioprocessings, which often involve organic compound/water mixtures.
Environmental sensors based on detecting fluorescence of an analyte are highly sensitive, thereby lowering detection limits. Different research groups have worked on the development of environmental sensitive sensors for detection of a great variety of organic compounds. For example, James et al. reported the combination of phenyl boronic acids and amine-substituents attached to fluorescent chromophores and utilized this for the detection of different saccharides. Other research groups developed similar sensoric compounds based on this platform (U.S. Pat. Nos. 6,627,177, 6,653,141, 6,673,625, 6,682,938, and 6,916,660). Arimori et al. reported fluorescent sensor molecules based on aliphatic amines with boronic acid and aromatic pendant groups (U.S. Pat. No. 6,740,257). Similarly, Daniloff et al. utilized the interaction of boronic acid and amine substituents of luminescent anthracene and naphthalene compounds for the detection of glucose in the presence of other alpha-hydroxy axids or beta-diketones (U.S. Pat. No. 6,800,451). Covin Jr. et al. utilized some europium-containing indicator monomers in conjunction with a water-soluble polymer (no conjugated polymer was used) for the detection of sugar analytes in environmental samples (U.S. Pat. No. 6,794,195).
Other applications requiring lower detection limits are warfare agents such as organophosphor esters (nerve gas) and nitroaromatics (explosives). Houser et al. utilized dentrimeric siloxane compounds, which are able to recognize the hydrogen-bonding accepting vapors of the warfare agents (U.S. Pat. No. 6,617,040). Similarly, McGill et al. reported linear and branched siloxane polymers, which work in the same way (U.S. Pat. No. 6,630,560).
Yet another field of applications for sensors is the detection of VOCs. The first example of the compounds exhibiting vapochromism were reported in the patent literature by Nagel (U.S. Pat. No. 4,826,774; 1989, Vapochromic double-complex salts). He utilized double complexes salts of platinum and palladium, which upon exposure to organic vapor show a color as well as a fluorescence change.
Lancaster et al. (U.S. Pat. No. 5,445,785; Volatile organic compound sensing devices) fabricated various apparatus using vapochromic substances having a composition of an inorganic double-complex salt. He apparently have not specified or included any structures or chemical composition into his patent.
Later, Mann et al. (U.S. Pat. No. 5,766,952; 1998, Vapochromic platinum-complexes and salts) invented platinum-platinum double complex salts and neutral platinum complexes, which exhibit again a change in color and luminescence.
More recently, Kato (U.S. Pat. No. 6,822,096; 2004, Environmental-sensitiv luminescent dimine-platinum binuclear complexes), utilized binuclear platinum (II) complexes, which did not only show a dark-red/light-red change of color but also a near-infrared/red change of luminescence via reversible adsorption of vapor of acetonitrile or ethanol, and therefore permitted the observation of on-off change of visually effective luminescence.
Other patents known to the applicants (U.S. Pat. Nos. 6,578,406; 6,338,977; 6,160,267 Vapochromic LED; U.S. Pat. Nos. 6,417,923; and 6,137,118 Vapochromic Photodiode) were all based on the platinum compounds described in U.S. Pat. No. 5,766,952 and described the fabrication of different devices utilizing the vapochromic behavior.
Many of the previously reported fluorescent materials focused on the detection of saccharides by the competing intramolecular interaction of an amine functionality with the boronic acid pendant. Less effort was spend on other biological compounds. Furthermore, the vapor-sensing compounds and devices are often manufactured from the expensive platinum salts and complexes and/or in combination with palladium. They based mainly on a color shift from dark-red to light-red, making it difficult to sense only by the eye. Sensors exhibiting an on-off change in their luminescent color rather then a color shift will be thus not only advantageous but also more sensitive. To applicants' knowledge the only known “on-off” example was shown by Kato (U.S. Pat. No. 6,822,096), who utilized the luminescence change from the invisible near-infrared to the visible red of binuclear platinum (II) complexes. Although these complexes seem to be an “on-off” sensor for the human eye, it only shifts the emitted wavelength out of the visible spectrum.